1. Field of the Invention
This invention relates to wire bonding devices that apply ultrasonic waves to connect chips having semiconductor elements to inner lead portions of leadframes by using metal fine wires in the assembly process of semiconductor devices. This application is based on patent application No. Hei 9-164741 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
The paper of Japanese Patent Application, Publication No. Hei 3-44051discloses an example of the wire bonding device.
FIG. 3 is a plan view showing a leadframe which is employed by the above wire boding device. Herein, a reference symbol "1" designates an island portion which has a square shape and which has multiple tab-hanging leads 1A. A reference symbol "2" designates inner lead portions that are arranged at periphery of the island portion 1. A reference symbol "3" designates outer lead portions that are arranged at periphery of the inner lead portions 2. A reference symbol "4" designates a frame that is constructed by outer frames 4A and inner frames 4B.
The inner lead portions 2 of the leadframe are arranged along a diagonal X, which connects intersection points formed between the outer frames 4A and the inner frames 4B. Herein, an angle .theta. formed between the diagonal X and a line Y, which is drawn to pass the tab-hanging leads 1A, is set at 45.degree..
FIG. 4 is a perspective view showing the aforementioned wire bonding device. Herein, a reference symbol "5" designates a heat stage that heats the leadframe. A reference symbol "6" designates a frame guide that transports and holds the leadframe. A reference symbol "7" designates an ultrasonic wave oscillator. A reference symbol "8" designates a bonding head. A reference symbol "9" designates an ultrasonic wave transmission arm, which is attached to the bonding head 8. A reference symbol "10" designates a bonding tool, which is attached to a tip portion of the ultrasonic wave transmission arm 9. Incidentally, a reference symbol "11" designates a connector wire, while "12" designates a chip having a semiconductor element.
In the wire bonding device whose construction is described above, the bonding tool 10 and the ultrasonic wave transmission arm 9 attached to the bonding head 8 generate ultrasonic waves, which are applied to the leadframe and the chip 12. Herein, an angle of 90.degree. is provided between an applying direction of the ultrasonic waves and a transportation direction of the frame 4. An overall shape of the leadframe is designed in such a way that all of the inner lead portions 2 and all of the outer lead portions 3 are both slanted by an angle of 45.degree. against the frame 4. Thus, it is possible to guarantee slanted transmission of the ultrasonic waves, which are transmitted to all of the inner lead portions 2 in their longitudinal directions by an angle of 45.degree..
The aforementioned wire bonding device has some problems, which will be described below.
A first problem is an increase of the cost for manufacturing the leadframes by the aforementioned wire bonding device. As a result, the manufacturing cost of the semiconductor device that is manufactured using the above leadframe becomes higher.
Because, the aforementioned wire bonding device is designed such that all of the island portion 1, inner lead portions 2 and outer lead portions 3 are slanted against the frame 4 by 45.degree.. For this reason, the leadframe requires "independent" parts for the outer lead portions, which are conventionally used as the common parts of the outer frame. So, the leadframe should increase the frame size and frame area.
A second problem is that the aforementioned wire bonding device requires specially designed leadframes, which are different from the conventional and generally designed leadframes. That is, the wire bonding device cannot use the conventional leadframes. For this reason, it is necessary to change the design of the leadframes and to re-manufacture the leadframes, which requires an enormous cost.
Because, the generally designed leadframe, which is conventionally used, is designed in such a way that all the inner lead portions and outer lead portions are slanted by an angle of 0.degree. or 90.degree. against the frame.